Dermatology Revision Guide ✅

🧴 Dermatology is visual medicine plus pattern recognition. Start by describing the lesion accurately, then ask: where is it?, what does it look like?, is it itchy, painful, scaly, blistering or systemic?, and is there infection, inflammation, allergy, autoimmunity or cancer? For exams, the key is to describe before diagnosing: site, size, colour, surface, border, distribution, arrangement and secondary change.

✅ 1. Describing Skin Lesions

🔍 1.1 Primary Lesions

• Macule: flat colour change less than 1 cm.
• Patch: flat colour change greater than 1 cm.
• Papule: raised solid lesion less than 1 cm.
• Plaque: raised flat-topped lesion greater than 1 cm.
• Nodule: deeper solid lesion, often palpable in dermis/subcutis.
• Vesicle: small fluid-filled blister less than 1 cm.
• Bulla: large fluid-filled blister greater than 1 cm.
• Pustule: pus-filled lesion.
• Wheal: transient oedematous raised lesion, typical of urticaria.

🧱 1.2 Secondary Changes

• Scale: excess keratin; seen in psoriasis, eczema, fungal infection.
• Crust: dried serum, blood or pus; honey-coloured crust suggests impetigo.
• Excoriation: scratch marks; indicates itch.
• Lichenification: thickened skin from chronic rubbing/scratching.
• Fissure: linear split in skin; common in eczema, psoriasis and tinea.
• Erosion: superficial loss of epidermis.
• Ulcer: deeper loss involving dermis; heals with scarring.
• Atrophy: thinning of skin; can occur with ageing, steroids or inflammatory disease.

🧠 Exam pearl: Dermatology marks are often won by description. “A well-demarcated erythematous plaque with silvery scale on the extensor elbow” is much stronger than simply writing “psoriasis”.

🧪 2. Dermatology Investigations

• Skin swab: useful if bacterial infection, weeping eczema or impetigo is suspected; interpret with clinical picture because colonisation is common.
• Skin scrapings: microscopy/culture for dermatophyte infection before prolonged antifungal treatment if diagnosis uncertain.
• Nail clippings: confirm fungal nail infection before oral antifungals.
• Wood’s lamp: can help with some pigment disorders and infections, but not definitive for most rashes.
• Dermoscopy: improves assessment of pigmented and non-pigmented skin lesions.
• Patch testing: delayed hypersensitivity testing for allergic contact dermatitis.
• Skin biopsy: used for uncertain diagnosis, suspected inflammatory dermatoses, vasculitis, blistering disease or malignancy.
• Blood tests: FBC, U&E, LFTs, CRP, autoimmune serology or viral testing depending on clinical context.

🧴 3. Eczema and Dermatitis

🌿 3.1 Atopic Eczema

Atopic eczema is a chronic inflammatory skin disease caused by impaired skin barrier function, immune dysregulation and itch-scratch cycling. It is associated with atopy, asthma, allergic rhinitis and food allergy in some patients.

• Symptoms: itch is essential; without itch, reconsider the diagnosis.
• Distribution: cheeks/extensor surfaces in infants; flexures, wrists, ankles, neck and hands in older children/adults.
• Acute eczema: red, itchy, weeping, vesicular and crusted.
• Chronic eczema: dry, scaly, lichenified and fissured.
• Triggers: soaps, fragrances, wool, heat, sweating, infection, stress, allergens and irritants.
• Complications: bacterial infection, eczema herpeticum, sleep disturbance, psychosocial impact.

💊 3.2 Eczema Management

• Use regular emollients generously and frequently, even when skin looks clear.
• Avoid soap; use soap substitutes and fragrance-free products.
• Topical corticosteroid potency should match site and severity.
• Use mild steroids on face/flexures unless advised otherwise; potent steroids are usually for thicker body skin and short courses.
• Topical calcineurin inhibitors can help sensitive sites or steroid-sparing strategies under appropriate guidance.
• Treat infected eczema if clinically infected, but avoid unnecessary antibiotics for colonisation alone.

⚠️ Safety pearl: Eczema herpeticum is a dermatological emergency. Suspect it if eczema becomes rapidly painful with punched-out erosions, fever or systemic illness; give urgent antiviral treatment and seek same-day specialist advice.

🧼 3.3 Contact Dermatitis

• Irritant contact dermatitis: direct skin barrier damage; common with handwashing, detergents, wet work and solvents.
• Allergic contact dermatitis: delayed type IV hypersensitivity; common triggers include nickel, fragrances, preservatives, rubber and hair dye.
• Distribution often matches exposure pattern, such as hands, eyelids, face or under jewellery.
• Management: identify/avoid trigger, emollients, topical steroids for flares, occupational advice and patch testing if recurrent.

🧬 4. Psoriasis

Psoriasis is an immune-mediated inflammatory skin disease with accelerated keratinocyte turnover. It is associated with psoriatic arthritis, metabolic syndrome, cardiovascular risk, depression and inflammatory bowel disease.

🔍 4.1 Clinical Features

• Classic plaque psoriasis: well-demarcated erythematous plaques with silvery scale.
• Common sites: elbows, knees, scalp, umbilicus, natal cleft and extensor surfaces.
• Nail signs: pitting, onycholysis, subungual hyperkeratosis, oil-drop discolouration.
• Guttate psoriasis: small “raindrop” papules after streptococcal infection, often in young people.
• Flexural psoriasis: shiny red plaques in skin folds with less scale.
• Pustular or erythrodermic psoriasis can be severe and systemic.

💊 4.2 Management

• Assess severity: body surface area, site, symptoms, functional impact and psychological impact.
• Topical therapy: emollients, topical corticosteroids, vitamin D analogues, coal tar or combination products depending on site.
• Scalp psoriasis often needs scale-softening treatment plus topical steroid/vitamin D preparations.
• Phototherapy may help widespread disease.
• Systemic therapy includes methotrexate, ciclosporin, acitretin and biologics under specialist care.
• Screen for psoriatic arthritis: joint pain, stiffness, dactylitis, heel pain and back pain.

🧠 Exam pearl: Psoriasis on the skin plus a swollen whole digit, nail pitting or heel pain should make you think of psoriatic arthritis, not “just skin disease”.

🌋 5. Acne, Rosacea and Hidradenitis

🌋 5.1 Acne Vulgaris

• Acne involves follicular plugging, sebum production, Cutibacterium acnes and inflammation.
• Lesions: open comedones, closed comedones, papules, pustules, nodules and cysts.
• Sites: face, chest and back.
• Assess severity, scarring risk and psychological distress.
• First-line options often combine topical retinoid, benzoyl peroxide and/or topical antibiotic depending on severity and contraindications.
• Avoid antibiotic monotherapy; combine with benzoyl peroxide where appropriate to reduce resistance.
• Oral isotretinoin is specialist-only and requires pregnancy prevention and monitoring due to teratogenicity and adverse effects.

🌹 5.2 Rosacea

• Chronic facial inflammatory condition affecting cheeks, nose, chin and forehead.
• Features: flushing, persistent erythema, telangiectasia, papules/pustules, burning/stinging and sensitive skin.
• No comedones - this helps distinguish rosacea from acne.
• Triggers: sunlight, heat, alcohol, spicy food, exercise, stress and topical steroids.
• Management: trigger avoidance, sun protection, gentle skincare, topical ivermectin/metronidazole/azelaic acid or oral tetracycline depending on phenotype/severity.
• Ocular rosacea causes gritty eyes, blepharitis and keratitis; refer if eye pain, photophobia or visual symptoms.

🕳️ 5.3 Hidradenitis Suppurativa

• Chronic inflammatory follicular occlusion disease affecting apocrine-bearing areas.
• Sites: axillae, groin, perineum, buttocks and inframammary folds.
• Features: painful nodules, abscesses, sinus tracts, scarring and malodorous discharge.
• Risk factors: smoking, obesity, family history, metabolic syndrome.
• Management: smoking cessation, weight support, antiseptic washes, topical/oral antibiotics, hormonal options, biologics or surgery in severe disease.

🦠 6. Bacterial Skin Infection

🍯 6.1 Impetigo

• Superficial bacterial infection, usually Staphylococcus aureus or Streptococcus pyogenes.
• Features: honey-coloured crusts, often around nose/mouth or exposed skin.
• Highly contagious; advise hygiene, avoid sharing towels, cover lesions where possible.
• Localised disease may be treated with topical therapy; widespread/systemic disease may need oral antibiotics according to local guidance.

🔥 6.2 Cellulitis and Erysipelas

• Cellulitis: deeper dermis/subcutaneous infection; usually unilateral, red, hot, swollen and painful.
• Erysipelas: more superficial with sharply demarcated raised edge.
• Risk factors: skin breaks, tinea pedis, oedema, venous disease, lymphoedema, obesity, diabetes.
• Assess severity: fever, tachycardia, hypotension, immunosuppression, rapidly spreading infection or severe pain.
• Management: antibiotics per local guidance, limb elevation, analgesia, treat portal of entry.
• Bilateral red legs are more often venous eczema, lipodermatosclerosis or oedema than bilateral cellulitis.

🚨 6.3 Necrotising Fasciitis

• Life-threatening deep soft tissue infection with rapidly progressive tissue necrosis.
• Red flags: severe pain out of proportion, rapid progression, systemic toxicity, skin necrosis, bullae, crepitus, anaesthesia over skin.
• Requires immediate surgical review, broad-spectrum IV antibiotics and resuscitation.
• Do not delay surgery for imaging if clinical suspicion is high.

🚨 Exam pearl: Pain out of proportion in a skin infection is necrotising fasciitis until proven otherwise.

🍄 7. Fungal and Parasitic Skin Disease

🍄 7.1 Dermatophyte Infection

• Tinea corporis: annular scaly plaque with active raised edge and central clearing.
• Tinea pedis: scaling, maceration and fissuring between toes or moccasin distribution.
• Tinea cruris: itchy groin rash with scaly advancing edge; usually spares scrotum.
• Tinea capitis: scalp scale, alopecia, broken hairs, lymphadenopathy; requires oral antifungal therapy.
• Confirm with scrapings if diagnosis uncertain or before prolonged oral therapy.

🍞 7.2 Candida

• Favours warm moist folds: groin, axillae, inframammary, abdominal folds and perineum.
• Features: bright red moist rash with satellite papules/pustules.
• Risk factors: diabetes, obesity, pregnancy, antibiotics, immunosuppression and incontinence.
• Management: reduce moisture/friction, topical antifungal, address underlying risk factors.

🪳 7.3 Scabies

• Infestation with Sarcoptes scabiei causing intense itch, often worse at night.
• Sites: finger webs, wrists, elbows, axillae, waist, buttocks, genitalia; infants may have palms/soles/scalp involvement.
• Burrows are diagnostic but often hard to find.
• Treat patient and close contacts at the same time, even if asymptomatic.
• Wash bedding/clothing or isolate items according to local advice; itch can persist for weeks after successful treatment.
• Crusted scabies is highly contagious and occurs in immunosuppressed/frail patients; needs urgent specialist/public health input.

🫧 8. Viral Skin Disease

🫧 8.1 Herpes Simplex

• Grouped painful vesicles on an erythematous base.
• Common sites: lips, genital area, fingers, eczema-affected skin.
• Primary infection can be severe with systemic symptoms and lymphadenopathy.
• Herpetic whitlow affects the finger and should not be incised.
• Eczema herpeticum is an emergency in atopic eczema.

⚡ 8.2 Shingles

• Reactivation of varicella zoster virus in a dermatomal distribution.
• Features: pain/burning followed by unilateral vesicular rash not crossing midline.
• Complications: post-herpetic neuralgia, ophthalmic involvement, Ramsay Hunt syndrome, disseminated infection in immunosuppression.
• Antivirals are most useful early, especially in older adults, severe pain/rash, ophthalmic shingles or immunosuppression.
• Ophthalmic shingles involving the tip of the nose suggests nasociliary involvement and needs urgent eye assessment.

🦪 8.3 Warts and Molluscum

• Warts are HPV-related keratotic papules; plantar warts interrupt skin lines and may show thrombosed capillaries.
• Molluscum contagiosum causes pearly umbilicated papules, common in children and atopic eczema.
• Most resolve spontaneously; treatment depends on symptoms, site, immune status and patient preference.

🌈 9. Pigmentary and Hair Disorders

🌈 9.1 Vitiligo

• Autoimmune loss of melanocytes causing well-demarcated depigmented patches.
• Common sites: face, hands, genital skin, around body openings and sites of trauma.
• Associated with autoimmune thyroid disease, type 1 diabetes and pernicious anaemia.
• Management: sun protection, camouflage, topical steroids/calcineurin inhibitors and phototherapy in selected cases.

🟤 9.2 Melasma and Post-Inflammatory Pigmentation

• Melasma: symmetrical brown facial hyperpigmentation, associated with pregnancy, hormonal therapy and UV exposure.
• Post-inflammatory hyperpigmentation follows acne, eczema, psoriasis, burns or procedures.
• Sun protection is essential; pigmentary change often improves slowly.

💇 9.3 Alopecia

• Alopecia areata: autoimmune non-scarring hair loss with smooth patches; exclamation mark hairs may be seen.
• Androgenetic alopecia: patterned hair thinning, common and genetically influenced.
• Telogen effluvium: diffuse shedding after stress, illness, childbirth, weight loss, iron deficiency or thyroid disease.
• Scarring alopecia destroys follicles and needs urgent dermatology assessment.

🧪 10. Urticaria, Angioedema and Drug Rashes

🪰 10.1 Urticaria

• Urticaria causes transient itchy wheals that usually resolve within 24 hours without bruising.
• Acute causes: viral infection, foods, medicines, insect stings or idiopathic.
• Chronic spontaneous urticaria lasts more than 6 weeks and often has no external allergy trigger.
• Management: non-sedating antihistamines, trigger avoidance where clear, and escalation under guidance if persistent.

🎈 10.2 Angioedema

• Deep swelling of lips, eyelids, tongue, airway or bowel wall.
• Histamine-mediated angioedema often occurs with urticaria and responds to antihistamines/adrenaline if anaphylaxis.
• Bradykinin-mediated angioedema, such as ACE inhibitor angioedema or hereditary angioedema, usually lacks urticaria and responds poorly to antihistamines/steroids.
• Airway symptoms require emergency assessment.

💊 10.3 Drug Eruptions

• Morbilliform drug eruption: widespread symmetrical maculopapular rash, often 1–2 weeks after starting a drug.
• Common triggers: antibiotics, anticonvulsants, allopurinol, NSAIDs and antiretrovirals.
• Red flags: mucosal involvement, blistering, skin pain, facial oedema, fever, eosinophilia, organ dysfunction.
• Severe reactions include SJS/TEN, DRESS and acute generalised exanthematous pustulosis.

🫧 11. Blistering and Severe Skin Reactions

🫧 11.1 Bullous Pemphigoid

• Autoimmune blistering disease, common in older adults.
• Features: tense blisters on itchy urticated or eczematous skin.
• Mucosal involvement is less common than pemphigus vulgaris.
• Diagnosis: biopsy for histology and direct immunofluorescence.
• Management: potent topical steroids or systemic therapy depending on severity.

🩸 11.2 Pemphigus Vulgaris

• Autoimmune intraepidermal blistering disease.
• Features: flaccid blisters, painful erosions and prominent oral mucosal involvement.
• Nikolsky sign may be positive.
• Can be life-threatening due to fluid loss and infection; needs urgent specialist management.

🚨 11.3 Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis

• Severe immune-mediated mucocutaneous reaction, usually drug-triggered.
• Features: fever, skin pain, targetoid lesions, blistering, epidermal detachment, mucosal erosions.
• Common triggers: allopurinol, anticonvulsants, sulfonamides, NSAIDs, antibiotics.
• Management: stop culprit drug, urgent hospital/burns/dermatology/ICU input, fluids, analgesia, wound and eye care.

🚨 Emergency pearl: A painful rash with mucosal involvement is not “just an allergy”. Think SJS/TEN and stop the suspected drug urgently while escalating care.

🩸 12. Purpura, Vasculitis and Ulcers

🟣 12.1 Purpura

• Purpura does not blanch because blood has leaked into skin.
• Causes: thrombocytopenia, platelet dysfunction, vasculitis, meningococcaemia, anticoagulants, trauma and senile purpura.
• Palpable purpura suggests small-vessel vasculitis.
• Non-blanching rash with fever or sepsis features is an emergency.

🩹 12.2 Leg Ulcers

• Check ABPI before compression therapy.
• Compression is key for venous ulcers if arterial supply is adequate.
• Refer urgently for suspected arterial compromise, rapidly enlarging ulcer, infection, malignancy or atypical ulcer.

☀️ 13. Sun Damage and Skin Cancer

☀️ 13.1 Actinic Keratosis and Bowen’s Disease

• Actinic keratosis: rough scaly sun-damaged lesion; premalignant risk for SCC.
• Bowen’s disease: SCC in situ; well-demarcated erythematous scaly plaque.
• Risk factors: UV exposure, fair skin, immunosuppression, outdoor work, age.

🦀 13.2 Basal Cell Carcinoma

• Most common skin cancer; locally invasive but rarely metastasises.
• Features: pearly papule, rolled edge, telangiectasia, central ulceration or non-healing lesion.
• Common on sun-exposed sites.
• Referral urgency depends on site, size, growth, symptoms and local pathways.

🧱 13.3 Squamous Cell Carcinoma

• Potential to metastasise, especially on lip/ear, immunosuppressed patients or high-risk tumours.
• Features: rapidly growing keratotic nodule, ulcer, tenderness or bleeding.
• Risk factors: UV exposure, actinic keratoses, immunosuppression, chronic wounds, HPV, arsenic.
• Usually needs urgent suspected cancer referral.

⚫ 13.4 Melanoma

• Melanoma arises from melanocytes and can metastasise early.
• ABCDE: Asymmetry, Border irregularity, Colour variation, Diameter >6 mm, Evolution/change.
• Other red flags: itching, bleeding, crusting, new lesion after age 40, “ugly duckling” lesion unlike others.
• Nodular melanoma may be symmetrical and fast-growing; think EFG - Elevated, Firm, Growing.
• Management: urgent suspected cancer referral for concerning pigmented lesions.

🧠 Exam pearl: “Evolution” is the most important melanoma clue. A changing lesion deserves respect even if it does not perfectly fit ABCD.

👶 14. Paediatric Dermatology

• Atopic eczema is common and intensely itchy; infection and sleep disturbance matter.
• Impetigo spreads rapidly in nurseries/schools and causes honey-coloured crusts.
• Hand, foot and mouth disease causes oral ulcers plus vesicles on hands/feet.
• Slapped cheek syndrome causes bright red cheeks then lacy rash; avoid exposure in pregnancy if non-immune.
• Chickenpox causes crops of itchy vesicles at different stages.
• Molluscum causes pearly umbilicated papules and is usually self-limiting.
• Non-blanching rash with fever requires urgent assessment for sepsis/meningococcaemia.

🚨 15. Dermatology Emergencies

📚 16. OSCE / Exam Pearls

• Itch is central to eczema; pain suggests infection, shingles or severe drug reaction.
• Psoriasis is well-demarcated, scaly and often extensor/scalp/nail-associated.
• Fungal rashes often have an active scaly edge with central clearing.
• Bilateral red legs are rarely bilateral cellulitis.
• Honey-coloured crusts suggest impetigo.
• Dermatomal vesicles suggest shingles.
• Non-blanching rash plus fever is sepsis until proven otherwise.
• Skin pain plus mucosal involvement suggests SJS/TEN.
• Changing pigmented lesion is melanoma until proven otherwise.
• Always ask about new drugs in any widespread rash.

📌 17. Quick Differentials Table

📚 References

• NICE. Acne vulgaris: management. NG198.
• NICE. Eczema - atopic: Clinical Knowledge Summary.
• NICE. Impetigo: antimicrobial prescribing. NG153.
• NICE. Cellulitis and erysipelas: antimicrobial prescribing. NG141.
• NICE. Melanoma: assessment and management. NG14.
• British Association of Dermatologists clinical guidelines should be checked for specialist pathways, biologics, isotretinoin, blistering disease and skin cancer management.
• Primary Care Dermatology Society guidance is useful for morphology-based clinical learning and primary care lesion recognition.

⚠️ Disclaimer

This article is for medical education and exam revision. Clinical decisions should follow current local guidelines, antimicrobial policies, pregnancy guidance, shared-care protocols, skin cancer referral pathways, formularies, senior advice and national guidance. Dermatology emergencies such as SJS/TEN, necrotising fasciitis, eczema herpeticum, meningococcal sepsis and severe angioedema require urgent senior input.